The present invention relates to packet data communications in cellular wireless communications.
Wireless packet data communication has become increasingly important. Indeed, with the tremendous increase in Internet users, packet-switched communication will likely become the dominant mode of communication as compared to the circuit-switched voice communications typically employed today. This trend has led to existing circuit-switched systems evolving to incorporate packet-switched communications. One well-known example is the extension of the Global System for Mobile (GSM) communications with General Packet Radio Services (GPRS).
GPRS is a packet switched system that uses the same physical carrier as the GSM cellular communication system and provides the same coverage as GSM. The GPRS radio interface is therefore based on a Time Division Multiple Access (TDMA) system with 200 kHz carriers divided into 8 time slots with Gaussan Minimum Shift Keying (GMSK) modulation. Each time slot typically serves a number of users, and one user can also be allocated more than one time slot to increase throughput over the air. The GPRS specification includes a number of different coding schemes that maybe used depending on the quality of the radio carrier.
To further increase the GPRS data throughput, a higher level modulation scheme, 8-Phase Shift Keying (8PSK), is being employed in Enhanced GPRS (EGPRS). Additional coding schemes developed for this 8-PSK offer efficient link adaptation, i.e., adapting coding and/or modulation based on present signal quality.
When running a Packet-Switched (PS) service in a GPRS network, a subscribed Quality of Service (QoS) must be supported. The Quality of Service (QoS) is negotiated when a mobile station requests activation of a Packet Data Protocol (PDP) context which is necessary in order to obtain a packet-switched service. In this PDP context activation process, one of the GPRS nodes engages in packet flow management procedures with the Base Stations System (BSS) of the traditional GSM system. In particular, the BSS creates a Packet Flow Context (PFC) with the requested quality of service for the packet flow involving the mobile station. In particular, the BSS checks whether the requested quality of service can be supported based on the condition of the cell in which the mobile station is currently located.
A problem with this PFC process is that the BSS is unaware of the mobile station's capabilities when negotiating the quality of service for the packet flow context. Absent mobile station capability information, (i.e., the radio capabilities of the mobile station), the BSS does not know what quality of service the mobile station is capable of supporting. As a result, the quality of service determined by the BSS for the packet flow context for the current cell may not be correct.
For example, if the requested quality of service for a packet flow includes a particular guaranteed bit rate or a particular maximum bit rate, the mobile station must be able to support those particular bit rates. If the BSS accepts too high of a bit rate, that high bit rate may not be supported by the mobile station when the data transmission begins for the packet flow. This may lead to a renegotiation of the quality of service, or the user may perceive an unacceptable quality of service.
For some services, a renegotiation of the quality of service is not acceptable. An example is a streaming service where a bit rate coding is selected at the start of the session. The selected bit rate coding is part of the quality of service requested at the PDP context activation. If the GPRS network accepts that quality of service, the streaming application will start running using the accepted bit rate coding. Because the mobile station can not support that bit rate coding, the BSS must renegotiate the quality of service at the actual start of the data transmission over the radio interface. In some situations, the mobile station application may not be able to accommodate the changed bit rate coding, leading possibly to disconnection of the session.